fix(gh): preserve valid completion cache on failure

plugins/gh/README.md

@@ -15,9 +15,6 @@ This plugin does not add any aliases.
 This plugin caches the completion script and is automatically updated when the
 plugin is loaded, which is usually when you start up a new terminal emulator.
 
-The cache is stored at:
-
-- `$ZSH/plugins/gh/_gh` completions script
-
-- `$ZSH_CACHE_DIR/gh_version` version of GitHub CLI, used to invalidate
-  the cache.
+The completion script is stored at `$ZSH_CACHE_DIR/completions/_gh`. If an
+update fails, the plugin keeps the last successfully generated completion
+script.

plugins/gh/gh.plugin.zsh

@@ -13,6 +13,12 @@ fi
 
 zmodload -F zsh/files b:zf_mv
 () {
-  local TMPPREFIX="$ZSH_CACHE_DIR/completions/_gh"
-  zf_mv -f -- =( gh completion --shell zsh ) "$TMPPREFIX"
+  local completion_file="$ZSH_CACHE_DIR/completions/_gh"
+  local completion_tmp="${completion_file}.$$.${RANDOM}"
+
+  if gh completion --shell zsh >| "$completion_tmp" && [[ -s "$completion_tmp" ]]; then
+    zf_mv -f -- "$completion_tmp" "$completion_file"
+  fi
+
+  command rm -f -- "$completion_tmp"
 } &|